Study finds climate change is increasing length of wildfire seasons across globe

[GliderGuider]

Study finds climate change is increasing length of wildfire seasons across globe

In a paper published Tuesday in the international journal Nature Communications, a team of researchers concluded that from 1979 to 2013, fire weather seasons have lengthened across 18.39 million square miles of Earth’s vegetated surface, resulting in an 18.7 percent increase in the global average fire season length. The global burnable area affected by long fire seasons has doubled in that time, and from 1996 until 2013 there has been a 53.4 percent increase in the frequency of long fire seasons.

The researchers found there are long-term steady increases in fire seasons in places that normally don’t see many fires, like the southeastern U.S., especially the coastal plains of Florida.

Steve Running, a regents professor of ecology at the University of Montana's College of Forestry and Conservation, said he was impressed by the thoroughness of the study.

"They've really done a comprehensive job," he said. "When you run three global data sets and they all say the same thing, that gives you more confidence that what you see is real. The fact that they looked at both the length of fire seasons and the amount of land area that is vulnerable to ignition is really kind of a space and time measurement combined, which is another reason why I saw this to be such a rigorous paper."

Running served on the Intergovernmental Panel on Climate Change that was awarded the 2007 Nobel Peace Prize. He said it was important that the paper made no projections into the future, but relied solely on data from the past.

"In my public talks, I always make a point of saying that climate change isn't a future projection, it actually started around 1980," Running explained. "It is interesting that this data set started in 1979. As I look over the past century, I can show three or four data sets that were stable until 1980, and then there is a pretty clear trend of data sets that started in a different trajectory. We saw a clear climate trend developing."

[Peacetrain]

1. We have a year round fire season out in the western states now

[OKIsItJustMe]

2. NASA Earth Observatory: Longer, More Frequent Fire Seasons

(Please note, source is NASA. Copyright concerns are nil.)

http://earthobservatory.nasa.gov/IOTD/view.php?id=86268&src=iotdrss

[font face=Serif][font size=5]Longer, More Frequent Fire Seasons[/font]



[font size=3]A new analysis of 35 years of meteorological data confirms fire seasons have become longer. Fire season, which varies in timing and duration based on location, is defined as the time of year when wildfires are most likely to ignite, spread, and affect resources.

In the map above, areas where the fire season lengthened between 1979 and 2014 are shown with shades of orange and red. Areas where the length of the fire season stayed the same are yellow. Shades of blue show where the fire season grew shorter. Gray indicates that there was not enough vegetation to sustain wildfires.

The analysis, led by U.S. Forest Service ecologist Matt Jolly, focused on four meteorological variables that affect the length of fire season: maximum temperatures, minimum relative humidity, the number of rain-free days, and maximum wind speeds. A combination of high temperatures, low humidity, rainless days, and high winds make wildfires more likely to spread and lengthens fire seasons. Jolly and colleagues used data from NOAA’s National Center for Environmental Prediction Reanalysis, NOAA’s NCEP-DOE Reanalysis, and the European Centre for Medium-Range Weather Forecasts Interim Reanalysis.

The researchers found that fire weather seasons have lengthened across one quarter of Earth’s vegetated surface. In certain areas, extending the fire season by a bit each year added up to a large change over the full study period. For instance, parts of the western United States and Mexico, Brazil, and East Africa now face wildfire seasons that are more than a month longer than they were 35 years ago.

The authors attribute the longer season in the western United States to changes in the timing of snowmelt, vapor pressure, and the timing of spring rains—all of which have been linked to global warming and climate change. On the other hand, the easing of droughts in Western Africa and the Pacific coast of South America likely contributed to the shortening of fire seasons in those areas.

In some parts of the world, tough fire seasons have also become more frequent. “The map at the top of the page depicts steady trends in season length, while the map below shows changes in variability,” explained Jolly. “In other words, the map below shows where long seasons are becoming more frequent, even if they aren’t becoming steadily longer.”



While many of the same areas that saw fire seasons grow progressively longer also faced more frequent fires seasons, the two measures differed significantly in some areas. Australia, for instance, has not experienced an increase in the length of fire seasons. However, eastern Australia has seen the years with long and severe fire seasons become more frequent.

Overall, 54 percent of the world’s vegetated surfaces experienced long fire weather seasons more frequently between 1996 and 2013 as compared with 1979-1996, according to Jolly. This amounted to a doubling in the total global burnable area affected by long fire weather seasons. (For this calculation, “long fire season” was defined as a length that was one standard deviation above the historical mean.)

It is important to note that although the study shows many environments have become more prone to fires, it does not demonstrate that the wildfires burned more intensely or charred more acres. That’s because even with longer and more frequent fire seasons, other factors can affect whether fires occur and how they behave, such as: whether lightning or human activity ignites the fires; whether humans attempt to suppress them; and whether there is enough fuel to sustain them.

References
Jolly, M. et al, (2015, July 14) Climate-induced variations in global wildfire danger from 1979 to 2013. Nature Communications, (6) 7537.

Further Reading
Scientific American (2015, July 14) More Wildfires Burning More Forest May Become the New Normal. Accessed July 21, 2015.
The Washington Post (2015, July 15) Scientists say the planet’s weather is becoming more conducive to wildfires . Accessed July 21, 2015.
Missoulan (2015, July 20) Missoula study: Climate change increasing length of wildfire seasons worldwide. Accessed July 21, 2015.

[font color="gray"]Earth Observatory maps by Joshua Stevens, using data provided by Matt Jolly, USDA Forest Service. Caption by Adam Voiland.

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